There was a time when it was not common for everybody to have baths in their houses and many people would make use of local Bath Houses for their regular ablutions. As bathrooms have become more common in houses so the need for Bath Houses has lessened and few still exist.
Another type of Bath House is one that is situated near natural mineral springs and are used for health and recreational purposes.
In other societies Bath Houses are used as spiritual or meeting places. See Wikipedia.
Buildings on this website of this type